2003
Volume
3, Number 3/4, pp. 78–81
G. Chkadua and Z. Kometiani
I.S. Beritashvili Institute of Physiology, Georgian Academy of Sciences, 14
Gotua St, 0160 Tbilisi, Georgia
Power parameters for the rate equations of enzymes with multiple ligand-binding sites
In the steady state the initial rate of action of
enzymes with multiple ligand-binding sites, as a function of ligand
concentration, can be given as the ratio of two polynomials. The minimum power n
of the numerator is always equal to the number of sites intended for essential activators.
The maximum powers of numerator and denominator represent respectively the sums
p = n + h + q(n+h)
and s = n + h + m + q(s), where h is
the number of sites for modifiers with a partial effect of activation or
inhibition, m is the number of sites for full inhibitors, and q(n+h) and q(k) are
integers that depend on the complexity of the molecular mechanism of the
enzyme, i.e. on the interactions of its allosteric sites. At rapid equilibrium q(n+h) = q(k) =
0. It should be noted that m
is not the sum of all the ligated sites that lead to dead-end branches in the
reaction scheme; some dead-end-producing ligated sites may not influence the
value of s.
Keywords: essential activators, full inhibitors and modifiers with a partial effect of activation and inhibition, multi-site enzymes.